Modern electronic radio devices use oscillators to generate clock signals needed in several different parts of the devices. For example, phase lock loops, modulators and demodulators and many digital base band components require clock signals.
It is typical for oscillators that in addition to the actual clock signal they also produce different harmonic frequencies. This is a feature of all oscillators. Harmonics are multiples of the actual clock signal frequency. Harmonics caused by clock signals may cause problems in sensitive radio frequency parts in radio devices, such as transceivers in cellular systems. For example, in transceivers of GSM cellular system, VCTCXO Oscillators are widely used (as 13MHz or 26MHz reference clocks, for example). Harmonics arising from the clock signal can be seen as reduced receiver sensitivity on some radio channels or as interference peaks in the receiver band noise spectrum.
Prior art offers some solutions to this problem. The alternatives have been filtering, tuning of the groundings on a printed board (PWB) and maximizing the isolation between the clock and sensitive parts. These solutions have so far provided only partial solution to the problem. It is not possible to isolate the harmonic signals completely from the radio frequency parts. Furthermore, this problem will get worse when development of device design moves towards so called system on chip (SoC) solutions where more and more blocks are placed very close to each other and isolation between noisy and sensitive blocks is reduced.